In 1254, a Buddhist monk returned to Japan from China and settled in Yuasa Town in the Wakayama Prefecture — he brought back with him new skills including a process for making miso. The liquid byproduct of the miso-making process would turn out to be modern soy sauce — consisting of soy beans, wheat, salt and water. The process for soy sauce making is both labor and time intensive and the artisan task has been passed down from generation to generation.
Simply put, the process starts with soy beans and roasted wheat in a koji mold where it is stored for four days to allow the koji starter to break down the sugar in the grain for fermentation. Then salt and water are mixed in and the mixture is transferred into large wooden barrels to ferment for 18 months to three and a half years. In this time span, the mixture is stirred constantly by hand. At the end of the fermentation period, the mixture is poured into cloth bags and nama soy sauce is extracted. Nama soy sauce is heated in traditional iron pots with red pine logs for over half a day with scum removed by hand before being bottled and shipped as soy sauce.
Check out the video by National Geographic and Mile Nagaoka above.